Embodiments of the present disclosure are directed to a fluidic control valve and, more specifically, to a valve which utilizes actuators having small displacements without the need for displacement amplification mechanisms. Some embodiments include components having both macro-scale and micro-scale features, such as features that are formed using micro-electromechanical systems (MEMS) device fabrication techniques. Fluidic control valves in accordance with other embodiments are also disclosed.
A microvalve is a miniature valve that controls the flow and/or pressure of a fluid passing through it. Inside the microvalve, the fluid flows through channels or orifices that are sized to a micrometer scale. Microvalves developed so far can be classified into two types: active and passive. Active microvalves utilize a powered actuator to control the opening and closure of the micro orifice or channel through which the fluid flows. Passive microvalves, on the other hand, have no actuator to control the fluid flow and are simply check valves operated by the pressure of the flowing fluid and its direction of flow. Passive microvalves are often used as part of micropumps. In contrast, active microvalves are usually free standing fluidic control devices.
The majority of active microvalves are used in pneumatic systems. Many of these valves are used in systems that require precision control of gas flow for biomedical and manufacturing processes. More recently, pneumatic active microvalves are seeing potential application in microspacecraft propulsion systems, where weight, volume and power savings are vital. Another promising application of pneumatic active microvalves is in human assist devices, where power consumption and weight should be minimized. A number of studies have also been conducted on microvalves for liquid applications. Most of these serve as check valves in micropumps or as valves in lab-on-a-chip and chemical analysis systems. However, despite continuous development for the past three decades, microvalves have seen limited commercial success due to difficulties in design such as pressure handling capacity, sealing and packaging.
Pneumatic valves utilizing piezoelectric actuators have recently entered the commercial market. Two variants on piezoelectric actuators are most commonly used: “piezostack” actuators and “piezobender” actuators. Piezostack actuators are composed of a stack of many layers of a piezoelectric material. They rely on the change in thickness of a piezoelectric material when a voltage is applied to produce a deflection. They produce relatively large forces but very small deflections. While variants of piezobender actuators exist, the most common is the “cantilevered piezobender”. It consists of a cantilever beam which includes a piezoelectric layer applied to either the top or bottom of a passive layer. When the piezoelectric layer is actuated, the strain induced in the layer causes the beam to deflect as a cantilever beam in pure bending. (An alternative architecture consists of using a piezoelectric layer on both the top and bottom surfaces of the beam. One layer is activated to place it in tension, while the opposite layer is activated so as to place it in compression, causing a larger deflection of the beam.) Piezobenders produce larger deflections but very small forces relative to piezostacks.
Current pneumatic valves exploit the benefits of these piezoelectric actuators. The Viva actuator of Parker Hannifin Corporation utilizes a piezostack actuator. This actuator requires the inclusion of a mechanical motion amplifier to increase the very small motion of the piezostack into a motion large enough to be useful with a single orifice.
Another pneumatic valve is the “VEMR” or “VEMC” series by Festo, which utilize cantilevered piezobenders rather than piezo stacks to achieve an actuator motion large enough to work with a single orifice. The use of piezobenders generally prevents the use of the valve as a proportional valve at high differential pressures (e.g., above 4 bar).